Electrochromic devices are attractive in green energy industries due to their low driving voltage and bistable properties. A major electrochromic material is inorganic oxide for longer lifetime and endurance, however, film thereof is prepared by using expensive processes and equipment such as vacuum deposition, spray pyrolysis, or sputtering. Even ignoring the cost of processing, the inorganic oxide still has shortcomings such as a slow electrochromic rate, less color variation, and the like. Most electrochromic organic materials use conjugated polymer with more color variation and fast electrochromic rates. However, the electrochromic conjugated polymer has shortcomings such as expensive monomers, a complicated synthesis, and formation by electro-polymerization. Therefore, the conjugated polymer with a low molecular weight has a size limited by the electrode size of the electro-polymerization. In other words, it is difficult to form an organic electrochromic material with a large area. On the other hand, the electrochromic conjugated polymer has an appearance of deep color due to its conjugated length. Although the deep color can be lightened by applying a voltage, the conjugated polymer cannot be fully transparent. In other words, the conjugated polymer must be electrified to effect a transparent state, thereby leading to the problem of high energy consumption.
Accordingly, a novel electrochromic organic material to meet the requirements of transparency, film-firming ability, and electrochromicity is called-for.